1. Field of the Invention
The present invention relates to a TAB (Tape Automated Bonding) type semiconductor device and, more particularly, to an improvement of connection portions between leads and lead frames of the semiconductor device.
2. Description of the Related Art
In a conventional TAB type semiconductor device, as expressed by its name, a semiconductor element is arranged on a tape (film), and a bonding operation can be performed by an automatic machine. It is expected that TAB type semiconductor devices will be popularly used due to their flexibility or the like.
That is, a conventional TAB type semiconductor device is arranged as shown in FIGS. 1 to 3, FIG. 1 is a sectional view showing a schematic overall arrangement of the semiconductor device, FIG. 2 is an enlarged plan view showing a 1/4 part of the device in FIG. 1, and FIG. 3 is an enlarged plan view showing a main part of the device in FIG. 2. As shown in FIG. 1, a conventional semiconductor device is constituted by a TAB tape 2 having an element through hole 1 and consisting of an insulator, a plurality of leads 3 consisting of a metal foil integrally formed on the TAB tape 2, a semiconductor element 4 arranged in the element through hole 1 and connected to one end of each of the leads 3 through a bump (not shown), a plurality of lead frames 5 each connected to the other end of a corresponding one of the leads 3, and a mold resin 6 sealed to cover the most part of the TAB tape 2, the leads 3, the semiconductor element 4, and the lead frames 5. Note that, in the mold resin 6, a resin positioned at the upper portion of the semiconductor element 4 and a resin positioned at the lower portion of the semiconductor element 4 have the same thickness L.
When the above semiconductor device is to be manufactured, one end of each of the leads 3 of the TAB tape 2 is connected to the semiconductor element 4 first. The semiconductor element 4 generally has Au bumps, and the leads 3 are Sn-plated. The leads 3 are heated by a bonding jig to form an Au--Sn alloy, thereby connecting the leads 3 to the semiconductor element 4. Each of the leads 3 of the TAB tape 2 is molded in a gull-wing shape, and cut to have a desired length. The leads 3 are laid on the lead frames 5, respectively and the positions of the leads 3 are respectively matched with the positions of the lead frames 5 such that the leads 3 overlap the lead frames 5. The lead frames 5 are generally Ag-plated, and the leads 3 are Sn-plated as described above. For this reason, when a bonding jig of about 550.degree. C..times.1" is pressed on the leads 3 and the lead frames 5, Ag--Sn diffusion progresses to respectively connect the leads 3 to the lead frames 5. When the resultant structure in this state is arranged in a transfer mold, and is subjected to transfer molding, the conventional semiconductor device is completed.
The lead frames 5 are arranged in a radial form to their distal ends, and the lead frames 5 overlap the leads 3 of the TAB tape 2 at the connection portions 7 to be connected to the leads 3, respectively. In this case, as shown in FIG. 3, the pitches of the lead frames 5 are drawn such that the lead width h of each of the lead frames 5 and each lead interval h' between the lead frames 5 assure a minimum width (0.22 or 0.27) at which etching or press processing can be performed, and a, b, c, d . . . are sequentially determined thereby setting the shape and size of each lead. Therefore, pitches between the leads satisfy a condition of P.sub.1 '&gt;P.sub.2 '&gt;. . . P.sub.n '. In accordance with this, the sizes of the leads 3 of the TAB tape 2 are determined accordingly.
In the conventional semiconductor device, however, the following drawback is posed. That is, the leads 3 of the TAB tape 2 are formed in a gull-wing shape, the pitches of the leads 3 are increased as the leads 3 become closer to the four corners of the semiconductor element 4, and the leads 3 are twisted and are not easily matched with the lead frames 5. In addition, the sizes of the pitches of the lead frames 5 and the sizes of the pitches of the leads 3 of the TAB tape 2 cannot easily be measured and managed because these pitches are not equal to each other. The lengths of the leads 3 of the TAB tape 2 tend to increase as the leads 3 become closer to the four corners of the semiconductor element 4. The leads 3 which are not formed in a gull-wing shape are used because the leads 3 of the TAB tape 2 cannot be stably formed in a gull-wing shape. For this reason, the thickness of the mold resin 6 at the upper portion of the semiconductor element 4 is increased, and passivation cracks disadvantageously occur.